rcu: Add call_rcu_tasks()

This commit adds a new RCU-tasks flavor of RCU, which provides
call_rcu_tasks().  This RCU flavor's quiescent states are voluntary
context switch (not preemption!) and userspace execution (not the idle
loop -- use some sort of schedule_on_each_cpu() if you need to handle the
idle tasks.  Note that unlike other RCU flavors, these quiescent states
occur in tasks, not necessarily CPUs.  Includes fixes from Steven Rostedt.

This RCU flavor is assumed to have very infrequent latency-tolerant
updaters.  This assumption permits significant simplifications, including
a single global callback list protected by a single global lock, along
with a single task-private linked list containing all tasks that have not
yet passed through a quiescent state.  If experience shows this assumption
to be incorrect, the required additional complexity will be added.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 2bb4c4f3531a..dffd9258ee60 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -117,6 +117,14 @@ extern struct group_info init_groups;
 #else
 #define INIT_TASK_RCU_PREEMPT(tsk)
 #endif
+#ifdef CONFIG_TASKS_RCU
+#define INIT_TASK_RCU_TASKS(tsk)                                        \
+        .rcu_tasks_holdout = false,                                     \
+        .rcu_tasks_holdout_list =                                       \
+                LIST_HEAD_INIT(tsk.rcu_tasks_holdout_list),
+#else
+#define INIT_TASK_RCU_TASKS(tsk)
+#endif
 
 extern struct cred init_cred;
 
@@ -224,6 +232,7 @@ extern struct task_group root_task_group;
         INIT_FTRACE_GRAPH                                               \
         INIT_TRACE_RECURSION                                            \
         INIT_TASK_RCU_PREEMPT(tsk)                                      \
+        INIT_TASK_RCU_TASKS(tsk)                                        \
         INIT_CPUSET_SEQ(tsk)                                            \
         INIT_RT_MUTEXES(tsk)                                            \
         INIT_VTIME(tsk)                                                 \